A sensitive liquid chromatographic procedure for the analysis of camphor in equine urine and plasma

A sensitive method was required to analyze low levels of camphor in equine urine and plasma. Camphorated oil (20% w/w camphor) was administered topically (6 g) and intratracheally (1 g) to standardbred mares. The drug was extracted from urine and plasma by diethyl ether and analyzed as its 2,4-dinitrophenylhydrazone derivative by reverse phase HPLC with UV detection. The UV detector was set at 368.5 nm and the samples were eluted from the C18 column by 82% acetonitrile in water. The detection limit achieved was about 10 ng/mL urine and about 20 ng/mL plasma. After topical administration, only trace amounts of camphor were found in urine, whereas in plasma detectable quantities appeared from 20 min to 12 hrs post-administration. After intratracheal administration, camphor appeared immediately in both urine and plasma and occurred in higher concentrations. The concentrations of camphor ranged from 11.4 to 21.6 ng/mL urine during 2 hrs post-administration and from 46.7 to 1650 ng/mL plasma during 1 hr. All traces of camphor disappeared from urine after 4 hrs and from plasma after 12 hrs. A GC/MS analysis of hydrolyzed urine extracts indicated two metabolites of camphor: trans-isoketopinic acid and an as yet uncharacterized hydroxycamphor.